1. Field of Invention
The present invention relates to a stray-light attenuating device. More particularly, the present invention relates to a stray-light attenuating device for a scanner.
2. Description of Related Art
Scanner is a common peripheral device in a computer system. Most platform type of scanners consists of a charge-coupled device (CCD) and a scanning drive system that commonly uses a stepping motor. In some applications, the CCD is fixed onto the scanning drive system so that a document is directly scanned. Alternatively, the CCD is fixed onto a stationary frame with light transmitted to the CCD via a set of optical lenses mounted on the scanning drive system.
In general, a CCD is able to take in a scanning line or a horizontal line of image data in each read operation. Each scanning line comprises of a plurality of pixels. Resolution of the scanning line depends on the density of CCD sensors. This type of resolution is commonly referred to as the horizontal resolution or the optical resolution. In the vertical direction, scanning is conducted through the driven CCD or driven optical lens system. Resolution is closely related to the step angle of the stepping motor and the accuracy of scanning drive system. This type of resolution is commonly referred to as the vertical resolution or the motor resolution. By conducting a vertical scanning, data from a number of horizontal lines are obtained. All line data can be subsequently combined to form a complete image.
Due to increasing demands for clearer image quality, scanners of higher resolution are always in need. In an image scanning operation, stray light is often one of the main causes of the lowering of signal power leading to poorer image resolution. Methods that can prevent the generation of stray light or remove any generated stray light is able to increase the signal-to-noise ratio and hence the quality of a scanner.
FIGS. 1 and 2 are cross-sectional side views of conventional stray-light attenuating devices in a scanner. As shown in FIG. 1, a plurality of stopping plates 114 is attached to the interior sidewalls of the scanner 100. A light source 106 emits a beam of light onto a document 120 to produce a reflected light 110. The light 110 is reflected by a reflecting mirror 108 to a lens 104. The lens 108 focuses the reflected light 110 onto an optical sensor 102 to produce an image. The optical sensor 102 can be a charge-coupled device (CCD). Stray light 112a from the light source 106 is reflected by the reflecting mirror 108 to the stopping plates 114. Stopping plates 114 is capable of dissipating stray light 112a, thereby serving as an isolator preventing any stray light 112a from passing through the lens 104 to the optical sensor 102. However, the stopping plates 114 is rather useless for stopping the passing of stray light 112b through the gaps between stopping plates 114 into the lens 104, thereby affecting image quality on the optical sensor 102.
As shown in FIG. 2, an alternative method of eliminating stray light is to add a few stopping plates 214axcx9c214c between lens 204 and optical sensor 202. The stopping plates 214axcx9c214c are attached to scanner 200. The stopping plates are erected in such a way that the plates closer to the optical sensor 202 such as stopping plate 214c have a greater height than the plates further out such as stopping plate 214a. Although this arrangement of stopping plates is able to filter most of the stray light 212b, a portion of stray light 212a still disperses into the optical sensor 202 affecting the quality of the image.
Accordingly, one object of the present invention is to provide a straylight attenuating device capable of preventing any stray light from entering charge-coupled device so that signal-to-noise ratio and hence quality of a captured image is increased.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a straylight attenuating device for removing stray light from a scanner. The attenuating device includes a light source, a lens, a reflecting mirror, a light sensor, a front cover plate and a back cover plate. The light source provides a beam of light for illuminating a document on the scanner. Light from the light source impinges upon the document and reflects to the reflecting mirror. The reflecting mirror turns the reflected light to the lens. The lens focuses the reflected light onto the optical sensor to form an image. The optical sensor can be a charge-coupled device having at least a plurality of connecting leads, a sensing surface and a backside. The back cover plate having an opening thereon is used for covering the backside of the optical sensor. The front cover plate having a window thereon is used for covering the sensing surface of the optical sensor.
According to this invention, a front cover plate is mounted onto the sensing surface of the optical sensor. A window on the front cover plate permits only the reflected light necessary for forming the image into the optical sensor. Efficiency of removing the stray light is increased the closer the front cover plate is moved towards the optical sensor. Hence, the front cover plate is either glued to the optical sensor or fastened to the back cover plate using a set of screws for easy assembling.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.